By Acacia Communications | Posted on January 24, 2018
Silicon photonics is the guiding of light in a planar arrangement of silicon-based materials to perform various functions. We focus here on the use of silicon photonics to create transmitters and receivers for fiber-optic telecommunications. As the need to squeeze more transmission into a given bandwidth, a given footprint, at a given cost increases, silicon photonics makes more and more economic sense.
Until circa 2002, fiber-optic communication for metropolitan distances (80—600 km) and long-haul distances (600–15,000 km) employed mostly simple on-off keying (OOK) transmission. On-off keying is simply turning on and off the light to transmit “1” s and “0” s. Higher performance, i.e., a lower bit-error rate (BER) for the same received optical power and/or for the same optical signal-to-noise ratio (OSNR), can be obtained by using phase-modulated formats, such as binary phase-shift keying (BPSK) or quadrature phase-shift keying (QPSK). They maximize the distance between constellation points for the same average signal power. In these “advanced” modulation formats , the term “symbol” is used to represent each data portion in time, because each symbol can carry multiple bits of information. Early BSPK and QPSK were detected by differential detection, i.e., by interfering one symbol with the previous symbol in an interferometer in the receiver.